1. Field of the Invention
The disclosed embodiments of the present invention relate to input apparatus, and more particularly, to a photo-sensor input apparatus capable of successfully detecting a touch event generated by a light pen as well as a touch event generated by a finger, and related display apparatus thereof.
2. Description of the Prior Art
An in-cell photo-sensor type touch apparatus determines if a touch input event has been detected based on the fact that a thin film transistor (TFT) photo sensor generates different photo currents in response to different light intensities. Please refer to FIG. 1A, which is a diagram illustrating a photocurrent Id generated from a TFT photo sensor 110 of a conventional photo-sensor type touch apparatus 100 in response to illumination. As shown in FIG. 1A, when the TFT photo sensor 110 is biased at a proper gate-to-source voltage Vgs, photoelectrons generated from the TFT photo sensor 110 due to the illumination may flow from the TFT photo sensor 110 to a capacitor 120 coupled between a voltage Va and a reference voltage node Vr. In other words, the photocurrent Id flows from the capacitor 120 to the TFT photo sensor 110, which causes variations in the voltage Va before and after the illumination. Therefore, the photo-sensor type touch apparatus 100 may enable a readout TFT 130 to read out a voltage variation value Vout of the voltage Va, thus allowing the backend circuits (not shown in FIG. 1A) to detect the touch input event.
Please refer to FIG. 1B and FIG. 1C together. FIG. 1B is a diagram illustrating different leakage currents Ids (i.e., the photocurrent Id at zero gate-to-source voltage Vgs) generated from the TFT photo sensor 110 without the applied gate-to-source voltage Vgs in cases where the photo-sensor type touch apparatus 100 is touched by a finger, illuminated by ambient light, and touched by a light pen. FIG. 1C is a diagram illustrating the relation between the photocurrent Id generated in various manners as shown in FIG. 1B and the gate-to-source voltage Vgs. As shown in FIG. 1B, in a case where an upper substrate 140 of the photo-sensor type touch apparatus 100 is touched by the finger, part of the ambient light is shielded. Therefore, the light intensity received by the TFT photo sensor 110 (disposed on a bottom substrate 150) is weaker as compared with a case where the TFT photo sensor 110 is illuminated by the ambient light, which is shown by the arrow L1 having a width narrower than that of the arrow L2. The leakage current Id a generated by the finger touch is thus smaller than the leakage current Id_b generated by the ambient light illumination. In another case where the photo-sensor type touch apparatus 100 is touched by the light pen, the light intensity received by the TFT photo sensor 110 is enhanced, which is shown by the arrow L3 having a width wider than that of the arrow L2. The leakage current Id_c generated by the light pen is thus higher than the generated leakage current Id_b. Ideally, as shown in FIG. 1C, by setting the gate-to-source voltage Vgs properly, the TFT photo sensor 110 is allowed to identify an input event triggered by the light pen touch and an input event triggered by the finger touch, simultaneously. However, due to certain factors such as the unstable ambient light, it is much difficult to find a voltage setting for identifying input events triggered by the finger touch, the ambient light illumination, and the light pen touch, simultaneously.
Please refer to FIG. 2A, which is a diagram illustrating the relation between the voltage signal intensities generated due to the illumination and the corresponding positions of TFT photo sensors in a photo-sensor type touch apparatus. Ideally, as shown in FIG. 2A, a difference level between the voltage signal generated by the light pen touch and the voltage signal generated by the finger touch as well as another difference level between the voltage signal generated by the finger touch and the voltage signal generated by the ambient light illumination are sufficient for the backend circuit to perform touch event detection. However, the ambient light level would change actually, and thus one of the above two difference levels is too small, which makes the photo-sensor type touch apparatus fail to detect touch input events (i.e., the input events triggered by the light pen touch and the finger touch) simultaneously. Please refer to FIG. 2B, which is a diagram illustrating the relation between the voltage intensity and the position in a case where the voltage (i.e., the gate-to-source voltage Vgs) of the TFT photo sensor is set properly for detecting the input event triggered by the light pen touch. As shown in FIG. 2B, it is difficult to identify voltage signals generated by the finger touch. Please refer to FIG. 2C, which is a diagram illustrating the relation between the voltage intensity and the position in a case where the voltage (i.e., the gate-to-source voltage Vgs) of the TFT photo sensor is set properly for detecting the input event triggered by the finger touch. Similarly, as shown in FIG. 2C, it is difficult to identify voltage signals generated by the light pen touch.
Thus, there is a need for an innovative photo-sensor type touch apparatus to solve the problem of identifying different types of input events (e.g., the input events triggered by the finger and the light pen).